The state of the art provides numerous techniques for manufacturing a printed circuit board. The starting material is a microelectronic substrate, typically a dielectric board such as, for example, an ABF (Ajinomoto Build-up Film) layer, which may then be processed according to one of the numerous techniques mentioned above to provide the printed circuit.
One such technique involves providing the dielectric layer, and then laser drilling via openings into the dielectric layer. Thereafter, the dielectric layer is roughened, subjected to chemical copper plating, such as electroless plating, to provide a thin layer of copper over the entire dielectric layer including on the walls of the via openings. A dry-film resist, or DFR, is then laminated onto the thin layer of copper, and the DFR thereafter subjected to an expose and develop process to form the circuit design pattern in accordance with the requirements of the circuit specifications. After subjecting the DFR to a developing solution in order to wash away exposed areas of the same, the combination of the dielectric layer-thin copper layer-patterned DFR is subjected to electrolytic copper plating in order to provide a copper layer (hereinafter “thick copper layer”) much thicker than the thin copper layer mentioned above both on regions of the thin copper layer not covered by the patterned DFR (in order to provide conductive traces on the dielectric layer), and, in addition, inside the via openings. Thus, after further plating of the thick copper layer to protect the same from etching, the patterned DFR is stripped from the combination to expose the thin copper layer not covered by the thick copper layer. The thus bare thin copper layer is now completely etched away down to the dielectric layer leaving a printed circuit board.
Another conventional technique for providing printed circuit boards involves the provision of a dielectric layer, such as an ABF layer, followed by a laser drilling process for providing via openings in the ABF layer. Thereafter, a DFR is laminated onto the dielectric layer, and the DFR thereafter subjected to an expose and develop process to form the circuit design pattern in accordance with the requirements of the circuit specifications. After subjecting the DFR to a developing solution in order to wash away exposed areas of the same, the combination of the dielectric layer-thin copper layer-patterned DFR is subjected to an etching process in order to ablate a predetermined thickness of the dielectric layer that remains uncovered by the patterned DFR, thus providing recesses within the dielectric layer corresponding to a location of the conductive traces to be provided on the dielectric layer. The patterned DFR is then stripped from the dielectric layer. Thereafter, the dielectric layer is subjected to electroless copper plating to provide a thin layer of copper over the entire dielectric layer including on the walls of the via openings and inside the recesses provided at the location of the traces. A thicker layer of copper is then provided onto the thin copper layer by way of electrolytic plating, and the thus formed combination subjected to either back etching, grinding or CMP in order to result in a printed circuit board.
Another known technique for providing interconnects according to the prior art is typically referred to as “Laser Embedded Technology,” or LET. In LET, laser ablation is used to provide via openings in a dielectric layer, such as an ABF layer. Thereafter, locations for the traces are ablated also using laser irradiation to provide recessed trace locations on the dielectric layer. Thereafter, electroless plating, and, thereafter, electrolytic plating with copper are provided on the thus ablated dielectric layer. Copper plating as described above results in the formation of a copper layer on the active surface of the dielectric layer, the copper layer filling the recessed trace locations and extending above the same. Thereafer, a process such as chemical mechanical polishing is used to remove the excess copper of the copper layer extending beyond the recessed trace locations, in this way resulting in the interconnects on the active surface of the dielectric layer.
However, disadvantageously, techniques of the prior art such as those described above, exhibit low throughput due to increased processing time, and, in addition, are ineffective for meeting current alignment budgets among others because they require the use of multiple processes for generating the vias and traces, which processes lead to a compounding of possible alignment errors.